The progression of senile cataracts is accompanied by an increase in the level of highly fluorescent yellow proteins. These proteins appear to be covalently crosslinked derivations of the normal lens proteins. It is proposed to isolate these proteins and to determine their origin by comparing them with proteins and their subunits isolated from the normal lens. It is intended to establish the structures of the fluorescent chromophore and the covalent crosslinks and to determine the amino acid sequences around these. Ultimately the whole sequence of these fluorescent proteins and for the protein from which they are derived, will be determined. Model systems will then be set up to study the formation of the crosslinks and fluorescence with the ultimate aim of developing a method for curing or arresting senile cataracts.